The invention relates to a method for metering and mixing different components according to the preamble of patent claim 1 as well as to an apparatus for carrying out this method.
With a known method of this kind (U.S. Pat. No. 5,464,283 A) a resin which forms the first component is continuously supplied in a predetermined quantity. The quantity of the continuously flowing paint stream is monitored and the required amount of a second component, namely solvents, is measured and introduced into a mixer in a predetermined ratio. The amount of solvent is controlled through valves and added in a predetermined ratio to the constant resin quantity which is measured by a through-flow meter. The resin and solvent are introduced together into the mixer in a predetermined fixed ratio.
It is absolutely essential to the functioning reliability of the method that the pressure of the solvent has always to be above the pressure of the resin.
With the known prior art there is always a specific differential pressure ratio maintained between the resin and the solvent. The corresponding differential pressure regulation serves especially to match the solvent pressure in dependence on the resin pressure. If through any type of influencing factor, for example through contamination or impurities it happens that the solvent pressure drops down to the pressure of the resin or below then the delivery process has to be terminated because the selected mixing ratio can no longer be observed in such an operating situation.
Two components are added to the resin in succession, namely a solvent and a hardener. After the resin is mixed with the solvent it forms a new starting component which is introduced into a second mixer as a new first component in a predetermined quantity. Also adding hardeners in the second mixer to the first component which is made up of the solvent and resin can only be carried out by introducing the first component from the first mixer in a predetermined quantity into the second mixer whilst the quantity of hardener is supplied into the second mixer in a correspondingly controlled or regulated manner. Also with this second method step the first component has always to be supplied constantly and the second component matched with this. Here also the delivery process has to be terminated if the selected mixing ratio cannot be observed in certain operating situations where the pressure of the hardener drops below the pressure of the first component.
There is also the fundamental drawback that the amount of hardener which is required is always metered in dependence on the associated amount of resin. During most of the operating time the amount of resin is therefore above the amount of hardener preset by the mixing ratio. This drawback is particularly damaging in the case of short spray intervals. It can only be overcome by a metering control with subsequent correction of the mixing ratio.
Starting from the prior art the object of the invention is to provide a method of the type already presumed known so that it is less susceptible to breakdown and the apparatus required for its implementation is functionally reliable so long as the components to be metered can be supplied, namely independently of which pressures prevail in the pipelines, which pressure differences are set and which viscosities the components have which are being metered.
This is achieved with the features of patent claim 1 and with an apparatus according to patent claim 5.
With the method according to the invention the quantities of the two components are regulated by pneumatically controlled valves. It is sufficient for the pneumatically controlled valves to only occupy two operating states, namely an opening position and a closing position. Each of the two pneumatically controlled valves then remains open until the predetermined amount corresponding to the desired mixing ratio has flowed through. It can be arranged so that the valve then still remains in the open position for a preset additional time. A deviation then takes place from the predetermined mixing ratio in the case of two components in the direction both of an excess of hardener and shortfall of hardener. At the start of metering the quantities of the two components are added up and corrected according to the mixing ratio set. The percentage deviation of the metering amount from the ideal value is constantly reduced through the growing overall amount.
Preferred designs of the invention are apparent from the sub-claims.